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Full text of "Text Book Of Mechanical Engineering"

838

Appendix II.

and represents a loss which is probably due to heating. Fig. 805
shews experiments on wires 28 feet long, where hysteresis is very
clear. The iron wire had a diameter of "049", and the steel
wire '045". (Seep. 1071.)

Influence of Temperature, on Strength.—This may be separately
considered for low and for high temperatures.

At low temperatures Professor Rudeloff tried seven different
materials :

1.  Rivet iron.

2.  Rolled iron.

3.  Hammered iron.

4.  Acid open-hearth steel.

5.  Basic Bessemer steel.

6.  Spring steel.
Crucible steel.

And the temperatures for every material were three,  64°, -,

cj, 806.  Ijif/buuenjce/ of Jtemji^xJbuur/& on

and - 100° Fahr. Measurements were made of ultimate tensile
strength, yield-point strength, and percentage elongation in 3^ ins.,
the results appearing in Fig. 806, where each specimen is numbered.
Much, apparently, depends on the chemical composition of the
material, but generally the ultimate strength is raised rapidly at
first and slowly afterward, the yield point slowly at first and rapidly
afterward, while percentage elongation is generally decreased.
The material is therefore less capable of resisting shock at low
temperatures. Professor Dewar finds a , strength increase of
50 to 100% at - 295° Fahr.

At high temperatures metals decrease both in strength and
ductility. Copper alloys become .much weaker, but cast iron is
little affected. Probably Professor Unwia. has given most